1. Field of the Invention
The present invention generally relates to a technology for performing user authentication based on fingerprints and specifically relates to detecting a counterfeit finger by using a sweep fingerprint sensor.
2. Description of the Related Art
Use of biometric information, such as fingerprints, for performing user authentication is becoming popular. It is said that the user authentication based on the biometric information is more reliable than the conventional method of using passwords or identification (ID) cards; because, while the passwords or the ID cards can be stolen or lost, the biometric information can not be stolen or lost. Even with the biometric information, however, there still is a possibility that a third person can maliciously pass as an authentic person.
In the case of a fingerprint for example, it is not very difficult to prepare a counterfeit finger that has the same fingerprint as that on a finger of an authentic user, and be successful in the user authentication by using the counterfeit finger. One approach to prevent that is to differentiate real fingers and counterfeit fingers, and not allow the use of the counterfeit fingers in the user authentication.
Counterfeit fingers can be made of silicon, rubber, gummy material (gelled gelatin solution) and the like. Silicon and rubber do not conduct electricity, so that counterfeit fingers made of silicon or rubber can be comparatively easily detected with capacitance fingerprint sensors or weak-electric-field fingerprint sensors. The gummy material, however, is very similar to the composition of human epidermis, moreover, it conducts electricity, which makes detection of the counterfeit fingers made of gummy material very difficult.
Japanese Patent Publication No. 2002-279413 discloses a technology for determining whether a finger is counterfeit based on a difference of featured information among a plurality of image frames serially acquired from a finger. This technology takes advantage of a phenomenon that the images gradually become clearer when serial images are taken of a real finger, while a counterfeit finger does not show such a transition.
Sweep fingerprint sensors are known in the art. A sweep fingerprint sensor has a reed shape, it acquires images of a fingerprint on a finger when the finger is slide, or “swept”, thereon, and based on the acquired images determines whether the fingerprint is authentic. The sweep fingerprint sensors are advantageous in that they are small and less expensive than other fingerprint sensors. However, the sweep fingerprint sensors have a disadvantage that they can not acquire an entire image of a finger at a time so that they are not suitable for the technology described in Japanese Patent Publication No. 2002-279413.
Thus, there is a need of a technology for accurately determining whether a finger used in fingerprint authentication is counterfeit by using a sweep fingerprint sensor.